There is a growing demand for steroid intermediates for the preparation of pharmaceutically active substances. This demand is increasingly met with cleavage products of sterols obtained by fermentation in aqueous nutrient solution. During such a microbial breakdown the sterols have been used in pure or very highly enriched form. Addition of emulsifying agents provides for a suitable distribution of the sterols in the aqueous nutrient solution. Such additives or accompanying substances in the sterols must induce the desired homogenization of the nutrient medium; however, they must not interfere with the growth of the microorganisms or with the desired breakdown of the sterols.
The preparation of pure sterol compounds of natural origin from vegetable and/or animal oils and/or fats, in which they are present in a low concentration as secondary substances, requires a complex process. According to British Pat. No. 489,623, natural fats or oils are subjected to molecular distillation. This results in a fraction enriched with sterol compounds, from which fraction the sterol can be obtained, if desired, by selective solvents, after saponification of the accompanying substances in the fraction. British Pat. No. 493,948 is also concerned, for example, with the distillation of sterol compounds under high vacuum. Here, the addition of carrier materials that have the same boiling range as the sterol compounds and are co-distilled with them is suggested for the distillation. These carrier materials must be capable of being separated subsequently from the sterol compounds by physical or chemical means.
A similar procedure is described in U.S. Pat. No. 2,146,894. According to the procedure disclosed, carrier materials of diverse origin are used to facilitate the distillation of natural substances with high boiling points under vacuum. Examples of such materials include fatty acids, esters such as aliphatic phthalates, benzyl phthalate, diglycerol tetrapropionate, mineral oil fractions, terpenes, and similar substances. Here, too, provisions are made for the separation of the co-distilled natural substance, and it is not detrimental when limited amounts of the natural substance remain in the carrier material, since this is to be reused.
In U.S. Pat. No. 4,148,810, a process for the isolation of sterols from distillation residues from the processing of fats is described. According to the process, the sterols are separated by transesterification with methanol and then isolated from the transesterification mixture by the formation of the adduct with calcium chloride in a aprotic solvent and with the small addition of a protic solvent.